Mark An object the sailing instructions require a boat to leave on a specified side, and a race committee boat surrounded by navigable water from which the starting or finishing line extends. An anchor line and objects attached temporarily or accidentally to a mark are not part of it.
The temporary part is a bit tricky. For instance a race committee boat at one end of the starting line. Before the five minute gun it isn't a mark. It's only an obstruction. The start line does not extent from one end, as long as the race hasn't begun. Therefore it's not a mark according to the definition.
After the start signal the committee boat only has a purpose as a mark, until all boats have started or - in most SIs - after five minutes. So the time the committee boat actually is a mark, according to the definition, is very short. What if someone attached a rubber boat at the stern in that period? Can you still maintain that it is attached only temporarily? Even if it's there for the whole starting procedure?
Most sailors will tell me that the rule prohibiting them from touching a mark is stupid. Most of the times it doesn't make a difference if they do or don't. The boom brushes along and that's it. They make sure that no part of the hull touches the mark, because that would slow them down. So why not scrap this rule - like in windsurfing?
From: 'Room at the Mark' by Robert C. MacArthur:
"One of the very first rules in yacht racing - when it was still in it's very first beginnings - only three members of the Yacht Club were skilled enough to race. This was before 1817 and before it became the Royal Yacht Club by decree of George IV. They sailed only speed races, sailing from A to B and back, so there was little need for rules. Depending on the wind direction a local work boat was hired to go to the desired location and anchor there as a mark. In one such a race the competitors found that they did have need for at least one rule. It was a hot day, and the man sitting as a mark had rigged a canvas awning over his cockpit to provide shade. One of the 125-foot cutters rounded so close that, while missing the boat itself, the end of her boom carried away the awning. The man was not amused. Henceforth, then, they would be most careful not to hit a mark. Otherwise, they might not be able to get anyone to sit for them."
Most rounding marks aren't boats anymore, and carry no people..... well, didn't the AC experiment with floating platform for photographers, just recently?
Anyway, starting vessels are frequently used as marks. I can assure you, the club member who's boat has been volunteered for that duty, is still NOT amused when someone hits it.
There are other arguments for not scrapping this rule. Like, if you can touch a mark, what prohibits a sailor from pushing a mark away to make room for his boat to round it at the right side?
A couple of weeks back I got a question about 'stand-off buoys" like an inner limit mark. They are there to keep boats away from the committee boat. They must be defined in the SI as such, as a mark with a required side, otherwise they are meaningless in the rulebook.
Note, you are allowed to touch the anchor line of a mark, but not the part that is underwater.
Picture off 'Bruno's buoy', way back in the good old days, when it was fun to follow the AC....